Method of cationic electrodeposition

ABSTRACT

An improved process for the preparation of cationic resins derived from polyepoxides is disclosed. Typically, the process comprises contacting the polyepoxide with particular polyether polyols and heating the two together to form a resin which may then be reacted with a cationic base group former such as an amine and acid. Aqueous dispersions of the cationic resins prepared by the improved process are useful for coating applications, particularly cationic electrodeposition. They exhibit good low temperature cure response and the cured coatings have good physical properties such as resistance to water, detergent and salt spray corrosion.

This is a division of application Ser. No. 301,712, filed Sept. 14, 1981U.S. Pat. No. 4,419,467 issued Dec. 6, 1983.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing cationicresins, to aqueous dispersions of the cationic resins, and to the use ofthese dispersions in cationic electrodeposition.

2. Brief Description of the Prior Art

Cationic electrodeposition resins are well known in the art. Forexample, U.S. Pat. No. 4,104,147 to Jerabek et al discloses cationicelectrodepositable resins which are formed from reacting a polyepoxidewith a primary or secondary amine and solubilizing the polyepoxide-amineadduct in aqueous medium with the aid of acid. The polyepoxide iscontacted and heated with a polymeric polyol, for example, a polyesterpolyol such as a polycaprolactone diol or a polyether polyol such aspolyoxytetramethylene glycol before reaction with the primary orsecondary amine.

U.S. Pat. No. 3,839,252 discloses quaternary ammonium saltgroup-containing resins which are formed from reacting a polyepoxidewith a tertiary amine salt. The polyepoxides are optionally contactedand heated with a polyether polyol such as polyoxypropylene glycol orpolyoxyethylene glycol before reaction with the tertiary amine salt.

U.S. Pat. No. 4,260,720 discloses cationic electrodepositable resinswhich are derived from a polymercapto-chain extended polyepoxide. Amongthe polyepoxides which may be used are polyglycidyl ethers of cyclicpolyols such as bisphenol A and 1,2-bis(hydroxymethyl)cyclohexane. Thesepolyepoxides can be produced by etherification of the cyclic polyol withepichlorohydrin in the presence of alkali. Besides bisphenol A and1,2-bis(hydroxymethyl)cyclohexane, oxyalkylated adducts of these cyclicpolyols such as ethylene oxide and propylene oxide adducts can be used.

SUMMARY OF THE INVENTION

The present invention relates to an improved process for preparing aresin which contains cationic base groups comprising reacting apolyepoxide resin with a cationic base group former. The improvement ofthe invention comprises contacting a polyepoxide with a polyether polyoland heating the two together to form the polyepoxide resin. Thepolyether polyol is formed from reacting:

(A) a cyclic polyol with

(B) ethylene oxide or a mixture of ethylene oxide and an alkylene oxidehaving 3 to 8 carbon atoms in the alkylene chain.

The present invention relates to a method of cationic electrodepositionand to coated articles derived therefrom. The method ofelectrodeposition involves coating a conductive substrate serving as acathode in an electrical circuit comprising said cathode and an anodeimmersed in an aqueous electrodepositable coating composition. Themethod involves passing electric current between the cathode and theanode to cause a coating to deposit on the cathode. The cationic coatingcomposition comprises a resin which contains cationic base groups whichis formed from reacting a polyepoxide resin with a cationic base groupformer. The polyepoxide resin is formed from reacting a polyepoxide witha polyether polyol. The polyether polyol is formed from reacting:

(A) a cyclic polyol with

(B) ethylene oxide or a mixture of ethylene oxide and an alkylene oxidehaving 3 to 8 carbon atoms in the alkylene chain. The equivalent ratioof (B) to (A) being within the range of 3 to 20:1. The curedelectrodeposited coatings have better water, detergent and salt spraycorrosion resistance, particularly when the coatings are cured at lowtemperature, than comparable coatings of the prior art.

DETAILED DESCRIPTION

The cationic resins of the present invention are non-gelled reactionproducts formed from contacting and heating together a polyepoxide witha polyether polyol, described in detail below, followed by reaction witha cationic base group former.

The cationic resins of the invention have high rupture voltages andthrowpower and deposit as films with improved flexibility. When comparedwith cationic products using polyester polyols such as described in U.S.Pat. No. 4,104,147, the products of the invention have improved saltspray corrosion resistance, particularly products which are cured at lowtemperature (300°-325° F. [149°-163° C.]). When compared with cationicproducts using polyalkylene ether polyols such as polypropylene glycol,polyoxyethylene glycol and polyoxytetramethylene glycol, as disclosed inU.S. Pat. Nos. 3,839,252 and 4,104,147, the products of the inventionshow improvement in alkali, water and salt spray corrosion resistance.

The polyepoxides which are used in the practice of the invention arepolymers having a 1,2-epoxy equivalency greater than one and preferablyabout two, that is, polyepoxides which have on an average basis twoepoxy groups per molecule. The preferred polyepoxides are polyglycidylethers of cyclic polyols. Particularly preferred are polyglycidyl ethersof polyhydric phenols such as bisphenol A. These polyepoxides can beproduced by etherification of polyhydric phenols with epihalohydrin ordihalohydrin such as epichlorohydrin or dichlorohydrin in the presenceof alkali. Examples of polyhydric phenols are2,2-bis(4-hydroxyphenyl)propane, 1,1-bis-(4-hydroxyphenyl)ethane,2-methyl-1,1-bis-(4-hydroxyphenyl)propane,2,2-bis-(4-hydroxy-3-tertiarybutylphenyl)propane,bis-(2-hydroxynaphthyl)methane, 1,5-dihydroxy-3-naphthalene or the like.

Besides polyhydric phenols, other cyclic polyols can be used inpreparing the polyglycidyl ethers of cyclic polyol derivatives. Examplesof other cyclic polyols would be alicyclic polyols, particularlycycloaliphatic polyols, such as 1,2-cyclohexanediol,1,4-cyclohexanediol, 1,2-bis(hydroxymethyl)cyclohexane,1,3-bis(hydroxymethyl)cyclohexane and hydrogenated bisphenol A.

Examples of other polyepoxides are polyglycidyl ethers of polyhydricalcohols, such as ethylene glycol, diethylene glycol, triethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol,1,5-pentanediol and the like.

The polyepoxides have molecular weights of at least 200 and preferablywithin the range of 200 to 2000, and more preferably about 340 to 2000.

The polyether polyol which is contacted and heated with the polyepoxideis formed from reacting a cyclic polyol with ethylene oxide oroptionally with a mixture of ethylene oxide and an alkylene oxide having3 to 4 carbon atoms in the alkylene chain.

The polyether polyol is prepared by techniques known in the art. Typicalreaction conditions are as follows: The cyclic polyol is charged to areactor capable of maintaining pressure. If the cyclic polyol is aliquid or low melting solid, for example, cyclohexanedimethanol, it canbe added to the reactor neat. If the cyclic polyol is a solid or a highviscosity liquid, it is preferably dissolved in a suitable solvent. Forexample, bisphenol A can be dissolved as a 50 percent solution in methylisobutyl ketone. Resorcinol can be dissolved in water. A catalyst suchas a tertiary amine, for example, N,N'-dimethylcyclohexylamine, or analkali metal hydroxide, for example, sodium hydroxide or potassiumhydroxide, is usually added to the reaction mixture in an amount ofabout 0.5 to 2 percent by weight based on total weight of the reactionmixture. The cyclic polyol is heated to about 180°-220° F. (82°-104° C.)and the reactor pressured with nitrogen to about 40-60 pounds per squareinch (psi).

Ethylene oxide also under pressure, usually at about 80-100 psi, is fedinto the reactor slowly in an incremental manner with cooling to removethe exothermic heat obtained when the ethylene oxide reacts with thecyclic polyol. Throughout the addition which lasts about 3 to 4 hours,the temperature of the reaction vessel is kept at about 180°-250° F.(82°-121° C.). At the completion of the ethylene oxide addition, thereaction mixture is held for about 1 to 2 hours at about 200°-250° F.(93°-121° C.) to complete the reaction. If solvent was present, it isstripped off and if sodium hydroxide or potassium hydroxide catalystwere used, they can be neutralized with acid, for example, phosphoricacid, and the salt filtered off.

If a mixture of ethylene oxide and higher alkylene oxide is used, thereaction preferably proceeds first with the higher alkylene oxide andthen with the ethylene oxide.

Examples of the cyclic polyols which can be used are polyhydric phenolsand cycloaliphatic polyols such as those mentioned above in connectionwith the preparation of the polyepoxides. Also, cyclic polyols such asthe aromatic diols, resorcinol, the aryl-alkyl diols such as the variousisomeric xylene diols and heterocyclic diols such as 1,4-piperizinediethanol can be used.

As mentioned above, besides ethylene oxide, mixtures of ethylene oxideand an alkylene oxide containing from 3 to 6, preferably 3 to 4 carbonatoms in the alkylene chain can be used. Examples of such alkyleneoxides are 1-2-propylene oxide, 1-methyl-1,2-propylene oxide,1,2-butylene oxide, butadiene monoepoxide, epichlorohydrin, glycidol,cyclohexane oxide and styrene oxide, with 1,2-propylene oxide beingpreferred.

The cyclic polyol-alkylene oxide condensate is preferably difunctionalor trifunctional, that is, it contains an average of 2 to 3 hydroxylgroups per molecule. Higher functional polyethers can be employed,although their use is not preferred because of gelation problems. Anexample of a higher functionality polyether would be the reactionproduct of a cyclic polyol such as sucrose with ethylene oxide.

The equivalent ratio of cyclic polyol to alkylene oxide should be withinthe range of 1:3 to 20, preferably 1:3 to 15. When the ratio is lessthan 1:3, the resultant coating has insufficient flexibility. When theratio is greater than 1:20, the electrical resistivity of the film willbe adversely affected resulting in lower rupture voltages andthrowpower, and the cured films will have poorer salt spray corrosionresistance.

The preferred cyclic polyol-alkylene oxide condensates used in thepresent invention are believed to have the following structural formula:

    R--(OX).sub.m (OC.sub.2 H.sub.4).sub.n --OH].sub.Z

where R is a cyclic radical, m is equal to 0 to 18, n is equal to 1 to15, n plus m is equal to 1 to 20, X is an alkylene radical of 3 to 8carbon atoms and Z is equal to 2 to 3.

The polyepoxide and the polyether polyol can be contacted by simplymixing the two together optionally in the presence of solvent such asaromatic hydrocarbons, for example, toluene, xylene and ketones, forexample, methyl ethyl ketone and methyl isobutyl ketone. The polyepoxideand the polyether polyol are heated together, preferably at atemperature of at least 75° C., more preferably at least 90° C. and mostpreferably about 100° to 180° C., usually in the presence of a catalystsuch as 0.05 to 2 percent by weight tertiary amines or quaternaryammonium bases. The time the polyepoxide and polyether polyol are heatedtogether with vary depending on the amounts contacted, how they arecontacted, the degree of agitation, temperature, and the presence ofcatalyst. In general, when the polyepoxide and polyether polyol arecontacted in an agitated reactor, they are heated for a time sufficientto increase the epoxy equivalency of the reaction mixture. Preferably,the epoxy equivalency should be increased at least 25, more preferablyat least 50, and most preferably from about 75-150 percent over itsoriginal value; the epoxide equivalent being determined according toASTM D-1652 (gram of resin solids containing 1-gram-equivalent ofepoxide).

Preferably, the ratio of equivalents of active hydrogen, e.g., hydroxyl,in the polyether polyol to equivalents of 1,2-epoxy in the polyepoxideshould be about less than 1, more preferably about 0.1 to about 0.8:1,most preferably 0.3 to 0.6:1.

The polyepoxide and the polyether polyol are contacted and heatedtogether to form a resinous reaction product or resin. Although thenature of the resinous reaction product is not completely understood, itis believed it is a mixture of about 15 to 45 percent by weight of achain-extended polyepoxide, that is, polyepoxide molecules linkedtogether with polyether polyol molecules and about 55 to 85 percent byweight of unreacted polyether polyol and unreacted polyepoxide orpolyepoxide reacted with itself.

The resinous reaction product is then reacted with a cationic groupformer, for example, an amine and acid. The amine can be a primary,secondary or tertiary amine and mixtures thereof.

The preferred amines are monoamines, particularly hydroxyl-containingamines. Although monoamines are preferred, polyamines such as ethylenediamine, diethylene triamine, triethylene tetraamine,N-(2-aminoethyl)ethanolamine and piperizine can be used but their use inlarge amounts is not preferred because they are multifunctional and havea greater tendency to gel the reaction mixture than monoamines.

Tertiary and secondary amines are preferred to primary amines becausethe primary amines are polyfunctional with regard to reaction to epoxygroups and have a greater tendency to gel the reaction mixture. Whenusing polyamines or primary amines, special precautions should be takento avoid gelation. For example, excess amine can be used and the excesscan be vacuum stripped at the completion of the reaction. Also, thepolyepoxide resin can be added to the amine to insure that excess aminewill be present.

Examples of hydroxyl-containing amines are alkanolamines,dialkanolamines, trialkanolamines, alkylalkanolamines, arylalkanolaminesand arylalkylalkanolamines containing from 2 to 18 carbon atoms in thealkanol, alkyl and aryl chains. Specific examples include ethanolamine,N-methylethanolamine, diethanolamine, N-phenylethanolamine,N,N-dimethylethanolamine, N-methyldiethanolamine and triethanolamine.

Amines which do not contain hydroxyl groups such as mono, di andtri-alkyl amines and mixed alkyl-aryl amines and substituted amines inwhich the substituents are other than hydroxyl and in which thesubstituents do not detrimentally affect the epoxy-amine reaction canalso be used. Specific examples of these amines are ethylamine,propylamine, methylethylamine, diethylamine,N,N-dimethylcyclohexylamine, triethylamine, N-benzyldimethylamine,dimethylcocoamine and dimethyltallowamine. Also, amines such ashydrazine and propylene imine can be used. Ammonia can also be used andis considered for the purposes of this application to be an amine.

Mixtures of the various amines described above can be used. The reactionof the primary and/or secondary amine with the polyepoxide resin takesplace upon mixing the amine with the product. The reaction can beconducted neat, or, optionally in the presence of suitable solvent.Reaction may be exothermic and cooling may be desired. However, heatingto a moderate temperature, that is, within the range of 50° to 150° C.,may be used to hasten the reaction.

The reaction product of the primary or secondary amine with thepolyepoxide resin attains its cationic character by at least partialneutralization with acid. Examples of suitable acids include organic andinorganic acids such as formic acid, acetic acid, lactic acid,phosphoric acid and carbonic acid. The extent of neutralization willdepend upon the particular product involved. It is only necessary thatsufficient acid be used to disperse the product in water. Typically, theamount of acid used will be sufficient to provide at least 30 percent ofthe total theoretical neutralization. Excess acid beyond that requiredfor 100 percent total theoretical neutralization can also be used.

In the reaction of the tertiary amine with the polyepoxide resin, thetertiary amine can be prereacted with the acid such as those mentionedabove to form the amine salt and the salt reacted with the polyepoxideto form the quaternary ammonium salt group-containing resin. Thereaction is conducted by mixing the amine salt and the polyepoxide resintogether in the presence of water. Typically, the water is employed onthe basis of about 1.75 to about 20 percent by weight based on totalreaction mixture solids.

Alternately, the tertiary amine can be reacted with the polyepoxideresin in the presence of water to form a quaternary ammonium hydroxidegroup-containing polymer which, if desired, may be subsequentlyacidified. The quaternary ammonium hydroxide-containing polymers canalso be used without acid, although their use is not preferred.

In forming the quaternary ammonium base group-containing polymers, thereaction temperature can be varied between the lowest temperature atwhich reaction reasonably proceeds, for example, room temperature, or inthe usual case, slightly above room temperature, to a maximumtemperature of 100° C. (at atmospheric pressure). At greater thanatmospheric pressure, higher reaction temperatures can be used.Preferably, the reaction temperature ranges between about 60° to 100° C.Solvent for the reaction is usually not necessary, although a solventsuch as a sterically hindered ester, ether or sterically hindered ketonemay be used if desired.

In addition to the primary, secondary and tertiary amines disclosedabove, a portion of the amine which is reacted with thepolyepoxide-polyether polyol product can be the ketimine of a polyamine.This is described in U.S. Pat. No. 4,104,147 in column 6, line 23, tocolumn 7, line 23, the portions of which are hereby incorporated byreference. The ketimine groups will decompose upon dispersing theamine-epoxy reaction product in water resulting in free primary aminegroups which would be reactive with curing agents which are described inmore detail below.

Besides resins containing amine salts and quaternary ammonium basegroups, resins containing other cationic groups can be used in thepractice of this invention. Examples of other cationic resins arequaternary phosphonium resins and ternary sulfonium resins as describedin U.S. Pat. Nos. 3,894,922 and 3,959,106, both to Wismer and Bosso.However, resins containing amine salt groups and quaternary ammoniumbase groups are preferred and the amine salt group-containing resins arethe most preferred.

The extent of cationic group formation of the resin should be selectedthat when the resin is mixed with aqueous medium, a stable dispersionwill form. A stable dispersion is one which does not settle or is onewhich is easily redispersible if some sedimentation occurs. In addition,the dispersion should be of sufficient cationic character that thedispersed resin particles will migrate towards the cathode when anelectrical potential is impressed between an anode and a cathodeimmersed in the aqueous dispersion.

In general, most of the cationic resins prepared by the process of theinvention contain from about 0.1 to 3.0, preferably from about 0.3 to1.0 milliequivalents of cationic group per gram of resin solids.

As indicated above, cationic resins of the present invention containactive hydrogens such as those derived from hydroxyl, primary andsecondary amino which make them reactive at elevated temperatures with acuring agent. The curing agent which is used should be one which isstable in the presence of the cationic resin at room temperature butreactive with the active hydrogens at elevated temperatures, that is,from about 90° to 260° C. to form a crosslinked product. Examples ofsuitable curing agents are aminoplast resins, capped isocyanates andphenolic resins such as phenol-formaldehyde condensates including allylether derivatives thereof.

The preferred curing agents are the capped isocyanates and these aredescribed in U.S. Pat. No. 4,104,147, column 7, line 36, continuing tocolumn 8, line 37, the portions of which are hereby incorporated byreference.

Sufficient capped polyisocyanate is present in the coating system suchthat the equivalent ratio of latent isocyanate groups to activehydrogens is at least 0.1:1 and preferably about 0.3 to 1:1.

Besides the blocked or capped isocyanates, aminoplast resins can also beemployed as curing agents in the practice of the present invention.Suitable aminoplasts for use with the reaction products are described inU.S. Pat. No. 3,937,679 to Bosso and Wismer in column 16, line 3,continuing to column 17, line 47, the portions of which are herebyincorporated by reference. As disclosed in the aforementioned portionsof the '679 patent, the aminoplast can be used in combination withmethylol phenol ethers. The aminoplast curing agents usually constitutefrom about 1 to 60 and preferably 5 to 40 percent by weight of theresinous composition based on total weight of aminoplast and thereaction product of a polyepoxide and amine. Also, mixed curing agentssuch as mixtures of capped isocyanates and aminoplast resins can beused.

The resins of the present invention are nongelled and are employed inthe form of aqueous dispersions. The term "dispersion" as used withinthe context of the present invention is believed to be a two-phase,transparent, translucent or opaque aqueous resinous system in which theresin is the dispersed phase and water is the continuous phase. Averageparticle size diameter of the resinous phase is generally less than 10and preferably less than 5 microns. The concentration of the resinousphase in the aqueous medium depends upon the particular end use of thedispersion and in general is not critical. For example, the aqueousdispersion preferably contains at least 0.5 and usually from about 0.5to 50 percent by weight resin solids. By non-gelled is meant thereaction products are substantially free of crosslinking and have anintrinsic viscosity when dissolved in a suitable solvent. The intrinsicviscosity of the reaction product is an indication of its molecularweight. A gelled reaction product, on the other hand, since it hasessentially infinitely high molecular weight, will have an intrinsicviscosity too high to measure.

Besides water, the aqueous medium may contain a coalescing solvent.Useful coalescing solvents include hydrocarbons, alcohols, esters,ethers and ketones. The preferred coalescing solvents include alcohols,polyols and ketones. Specific coalescing solvents include isopropanol,butanol, 2-ethylhexanol, isophorone, 4-methoxy-2-pentanone, ethylene andpropylene glycol, and the monoethyl, monobutyl and monohexyl ethers ofethylene glycol. The amount of coalescing solvent is not unduly criticaland is generally between about 0.01 and 40 percent by weight, preferablyabout 0.05 to about 25 percent by weight based on total weight of theaqueous medium.

In some instances, a pigment composition and, if desired, variousadditives such as plasticizers, surfactants or wetting agents areincluded in the dispersion. The pigment composition may be any of theconventional types, comprising, for example, iron oxides, lead oxides,strontium chromate, carbon black, coal dust, titanium dioxide, talc,barium sulfate, as well as color pigments such as cadmium yellow,cadmium red, chromium yellow and the like. The pigment content of thedispersion is usually expressed as pigment-to-resin ratio. In thepractice of the invention, the pigment-to-resin ratio is usually withinthe range of 0.02 to 1:1. The other additives mentioned above areusually in the dispersion in amounts of 0.01 to 10 percent by weightbased on total weight of resin solids.

Also, soluble lead such as lead acetate may be added to the dispersion.See, for example, U.S. Pat. No. 4,115,226 to Zwack and Jerabek.

When the aqueous dispersions as described above are employed for use inelectrodeposition, the aqueous dispersion is placed in contact with anelectrically conductive anode and an electrically conductive cathodewith the surface to be coated being the cathode. Following contact withthe aqueous dispersion, an adherent film of the coating composition isdeposited on the cathode when a sufficient voltage is impressed betweenthe electrodes. The conditions under which the electrodeposition iscarried out are, in general, similar to those used in electrodepositionof other types of coatings. The applied voltage may be varied and canbe, for example, as low as one volt to as high as several thousandvolts, but typically between 50 and 500 volts. The current density isusually between 0.5 ampere and 15 amperes per square foot and tends todecrease during electrodeposition indicating the formation of aninsulating film.

The aqueous resinous dispersions of the present invention can also beused in other conventional coating applications such as flow, dip, sprayand roll coating applications. For electrodeposition and the otherconventional coating applications, the coating compositions can beapplied to a variety of electroconductive substrates especially metalsuch as steel, aluminum, copper, magnesium and the like, but alsoincluding metallized plastic and conductive carbon-coated materials. Forthe other conventional coating applications, the compositions can beapplied to the non-metallic substrates such as glass, wood and plastic.

After the coating has been applied by electrocoating or otherconventional coating applications, it is cured usually by baking atelevated temperatures such as 90° to 260° C. for about 1 to 30 minutes.

Illustrating the invention are the following examples, which, however,are not to be construed as limiting the invention to their details. Allparts and percentages in the examples as well as throughout thespecification are by weight unless otherwise indicated.

Vehicle Resins Example A

The following example shows the preparation of a cationicelectrodepositable resin which was formed by contacting and heatingtogether a polyglycidyl ether of bisphenol A with a bisphenol A-ethyleneoxide adduct (1/10 molar ratio) to form a polyepoxide resin, followed byreacting the resin with a mixture of secondary amines. The aminereaction product is then combined with a blocked isocyanate crosslinkingagent, partially neutralized with acid and dispersed in deionized water.The cationic electrodepositable resin was prepared from the followingmixture of ingredients:

    ______________________________________                                        Ingredients    Parts by Weight                                                                           Solids  Equivalents                                ______________________________________                                        EPON 829.sup.1 727.6       702.1   3.735                                      Adduct of bisphenol A-                                                                       303.2       303.2   1.000                                      ethylene oxide (1/10                                                          molar ratio)                                                                  Xylene         37.8                                                           Bisphenol A    197.8       197.8   1.735                                      Benzyldimethylamine                                                                          3.6                                                            Blocked isocyanate                                                                           1016.3      711.4                                              crosslinker.sup.2                                                             Diketimine derivative.sup.3                                                                  73.06       53.1    0.609                                      N--methylethanolamine                                                                        65.0        65.0    0.865                                      1-phenoxy-2-propanol                                                                         101.6                                                          ______________________________________                                         .sup.1 Epoxy resin solution made from reacting epichlorohydrin and            bisphenol A having an epoxy equivalent of 188 commercially available from     Shell Chemical Company.                                                       .sup.2 Polyurethane crosslinker formed from halfcapping toluene               diisocyanate (80/20 2,4/2,6-isomer mixture) with 2hexoxyethanol and           reacting this product with trimethylolpropane in a 3:1 molar ratio. The       crosslinker is present as a 70 percent solids solution in methyl isobutyl     ketone and butanol (9:1 weight ratio).                                        .sup.3 Diketimine derived from diethylenetriamine and methyl isobutyl         ketone (73 percent solids in methyl isobutyl ketone).                    

The EPON 829, bisphenol A-ethylene oxide adduct and xylene were chargedto a reaction vessel and heated together with nitrogen sparge to 210° C.The reaction was held at 200°-215° C. with refluxing to remove any waterpresent. The ingredients were cooled to 150° C. and the bisphenol A and1.6 parts of the benzyldimethylamine (catalyst) added. The reactionmixture was heated to 150° C. and held between 150° and 190° C. forabout 1/2 hour and then cooled to 130° C. The remaining portion of thebenzyldimethylamine catalyst was added and the reaction mixture held at130° C. for about 21/2 hours until a reduced Gardner-Holdt viscosity (50percent resin solution in 2-ethoxyethanol) of H was obtained. Note, thereaction sequence is believed to be the EPON 829 reacting first withbisphenol A to form a polyepoxide with an epoxide equivalent of about600, followed by heating with the bisphenol A-ethylene oxide adduct toan epoxide equivalent of about 990. The polyurethane crosslinker, thediketimine derivative and the N-methylethanolamine were then added andthe temperature of the reaction mixture brought to 110° C. and held atthis temperature for one hour. The 1-phenoxy-2-propanol was added andthen 2200 parts of the reaction mixture was dispersed in a mixture of30.9 grams acetic acid, 44.3 grams of the surfactant mixture describedin Example B, infra, and 2718 grams of deionized water. The solidscontent of the aqueous dispersion was 35.5 percent. This dispersion wasthen diluted to 32 percent solids and the solvent removed by vacuumdistillation at 85°-90° C. The solids of the solvent stripped dispersionwas about 36 percent.

Example B

A cationic electrodepositable resin similar to Example A was preparedwith the exception that a bisphenol A-ethylene oxide condensate having amolar ratio of 1/7 was used.

    ______________________________________                                        Ingredients            Parts by Weight                                        ______________________________________                                        EPON 829               114.0                                                  Bisphenol A-ethylene oxide adduct (1/7                                                               38.0                                                   molar ratio)                                                                  Xylene                 5.4                                                    Bisphenol A            31.0                                                   Benzyldimethylamine    0.6                                                    Crosslinker of Example A                                                                             139.6                                                  Diketimine of Example A                                                                              11.9                                                   N--methylethanolamine  9.3                                                    1-phenoxy-2-propanol   14.7                                                   Acetic acid            5.2                                                    Surfactant.sup.1       7.2                                                    Deionized water        408.0                                                  ______________________________________                                         .sup.1 Cationic surfactant prepared by blending 120 parts of alkyl            imidazoline commercially available from Geigy Industrial Chemicals as         GEIGY AMINE C, 120 parts by weight of an acetylenic alcohol commercially      available from Air Products and Chemicals Inc. as SURFYNOL 104, 120 parts     by weight of 2butoxyethanol and 221 parts by weight of deionized water an     19 parts of glacial acetic acid.                                         

The procedure for preparing the resinous composition was as generallydescribed in Example A except that the EPON 829, bisphenol A andbisphenol A-ethylene oxide adduct were heated together to a reducedGardner-Holdt viscosity of K instead of H. The increase in epoxyequivalent was from about 600 to 950. Ninety-seven and one-half (971/2)percent by weight of the resin was dispersed in the mixture of aceticacid, surfactant and deionized water as described in Example A. Theorganic solvent was removed by vacuum distillation as described inExample A.

Example C

The following example shows the preparation of a cationicelectrodepositable resinous composition similar to Example A with theexception that a bisphenol A-propylene oxide-ethylene oxide adduct(1/2/4 molar ratio) was employed.

    ______________________________________                                        Ingredients              Parts by Weight                                      ______________________________________                                        EPON 828.sup.1           702.2                                                Bisphenol A-propylene oxide-ethylene oxide                                                             243.1                                                adduct (1/2/4 molar ratio) (OH value = 230)                                   Xylene                   60.2                                                 Bisphenol A              197.8                                                Benzyldimethylamine      3.8                                                  Polyurethane crosslinker of Example A                                                                  991.3                                                Diketimine derivative of Example A                                                                     72.5                                                 N--methylethanolamine    65.0                                                 1-phenoxy-2-propanol     97.7                                                 ______________________________________                                         .sup.1 Epoxy resin solution made from reacting epichlorohydrin and            bisphenol A having an epoxy equivalent of about 188, commercially             available from Shell Chemical Company.                                   

The procedure for preparing the resinous composition was as generallydescribed in Example A with the exception that the EPON 828, bisphenol Aand bisphenol A-propylene oxide-ethylene oxide adduct were heatedtogether to a Gardner-Holdt reduced viscosity of N-O. The increase inepoxy equivalent was from about 570 to 1024. The reaction mixture (2100parts by weight) was dispersed in 30.6 parts of acetic acid and 42.2parts of the surfactant mixture of Example B and 2564.6 parts ofdeionized water. The solvent was removed as described in Example A andthe final dispersion had a solids content of 38.1 percent.

Example D

A cationic electrodepositable resinous composition similar to that ofExample A was prepared with the exception that a resorcinol-ethyleneoxide condensate (1/6.5 molar ratio) was used.

    ______________________________________                                        Ingredients              Parts by Weight                                      ______________________________________                                        EPON 829                 727.6                                                Resorcinol-ethylene oxide (1/6.5 molar ratio)                                                          183.9                                                (OH value = 305)                                                              Xylene                   31.5                                                 Bisphenol A              197.8                                                Benzyldimethylamine      3.6                                                  Polyurethane crosslinker of Example A                                                                  946.8                                                Diketimine derivative of Example A                                                                     76.0                                                 N--methylethanolamine    65.0                                                 1-phenoxy-2-propanol     93.4                                                 ______________________________________                                    

The procedure for preparing the resinous composition was as generallydescribed in Example A with the exception that the reaction was held fora reduced Gardner-Holdt viscosity of N. The increase in epoxy equivalentwas from about 540 to 901. The reaction mixture (2000 parts) wasdispersed in a mixture of 30.5 parts acetic acid, 40.2 parts of thesurfactant mixture of Example B and 2459 parts of deionized water. Thesolvent was removed as described in Example A. The final dispersion hada solids content of 36.9 percent.

Example E

A cationic electrodepositable resinous composition similar to Example Awas prepared with the exception that a cyclohexanedimethanolethyleneoxide adduct (1/6.5 molar ratio) was used.

    ______________________________________                                        Ingredients              Parts by Weight                                      ______________________________________                                        EPON 828                 702.2                                                Cyclohexanedimethanol-ethylene oxide adduct                                                            183.9                                                (1/6.5 molar ratio)                                                           Xylene                   57.0                                                 Bisphenol A              197.8                                                Benzyldimethylamine      3.6                                                  Polyurethane crosslinker of Example A                                                                  945.4                                                Diketimine derivative of Example A                                                                     73.6                                                 N--methylethanolamine    65.0                                                 1-phenoxy-2-propanol     93.2                                                 ______________________________________                                    

The procedure for preparing the resinous composition was as generallydescribed in Example A with the exception that the reaction was held foran R Gardner-Holdt reduced viscosity. The increase in epoxy equivalentwas from about 540 to 949. The reaction mixture (2000 parts) wasdispersed in a mixture of 30.5 parts acetic acid, 40.2 parts of thesurfactant mixture of Example B and 2460 parts of deionized water. Thesolvent was removed as described in Example A and the final dispersionhad a solids content of 36.9 percent.

Example F

A cationic (quaternary ammonium salt group) electrodepositable resinouscomposition was prepared by contacting and heating together apolyepoxide and a bisphenol A-ethylene oxide adduct (1/10 molar ratio),combining the product with a blocked isocyanate crosslinker, reactingwith a tertiary amine acid salt and dispersing the reaction product inwater.

    ______________________________________                                                                            Parts by                                  Ingredients       Solids  Equivalents                                                                             Weight                                    ______________________________________                                        EPON 829          541.4   2.85      561.1                                     Bisphenol A       176.6   1.54      176.6                                     Xylene                              4.9                                       TEXANOL.sup.1                       53.7                                      Bisphenol A-ethylene oxide                                                                      182.0   0.60      182.0                                     adduct (1/10 molar ratio)                                                     Benzyldimethylamine                                                                             2.0               2.0                                       TEXANOL                             26.7                                      Lactic acid       3.3               3.8                                       INDOPOL L-14.sup.2                                                                              31.8              31.8                                      2-phenoxyethanol                    166.5                                     Polyurethane crosslinker.sup.3                                                                  353.7             525.6                                     Lactic acid salt of                                                                             33.5    0.168     44.7                                      dimethylethanolamine.sup.4                                                    Lactic acid salt of                                                                             75.5    0.335     100.6                                     dimethylcyclohexylamine.sup.5                                                 GEIGY AMINE C     7.5     0.027     7.5                                       Deionized water                     70.0                                      ______________________________________                                         .sup.1 2,2,4trimethylpentane-1,3-diol monoisobutyrate commercially            available from Eastman Chemical Company.                                      .sup.2 Polybutene commercially available from Amoco Chemical Corp.            .sup.3 2butoxyethanol fully blocked polymethylene polyphenyl isocyanate a     a 68 percent solids solution in 2butoxyethanol.                               .sup.4 75 percent solids solution in isopropyl alcohol.                       .sup.5 75 percent solids solution in water.                              

The EPON 829, bisphenol A and xylene were charged to a reaction vesseland heated under a nitrogen blanket to 150° C. to initiate an exotherm.The reaction mixture was permitted to exotherm for about one hour withthe highest temperature reaching 185° C. The reaction mixture was cooledto 169° C. followed by the addition of the bisphenol A-ethylene oxideadduct and the first portion of TEXANOL. The benzyldimethylamine wasadded and the reaction mixture was held between 126° and 134° C. forabout 5 hours until the reaction mixture had a reduced Gardner-Holdtviscosity (50/50 blend in 2-ethoxyethanol) of P-Q. The increase in epoxyequivalent was from about 550 to 1234. At that point, the second portionof TEXANOL, the lactic acid, the INDOPOL L-14, the polyurethanecrosslinker, the 2-phenoxyethanol, the dimethylethanolamine anddimethylcyclohexylamine lactate salts, the GEIGY AMINE C and thedeionized water were added and the reaction mixture heated to 80° C. andheld for 2 hours. The reaction mixture was then thinned with deionizedwater to a solids content of 32 percent. The resinous dispersioncontained 0.389 milliequivalents per gram solids of quaternary ammoniumbase groups.

EXAMPLE G

A cationic electrodepositable resin similar to Example F was preparedwith the exception that an adduct of bisphenol A-ethylene oxide (1/6molar ratio) was used.

    ______________________________________                                                                    Parts by                                          Ingredients                 Weight                                            ______________________________________                                        EPON 829                    561.1                                             Bisphenol A                 176.6                                             Xylene                      4.9                                               TEXANOL                     53.7                                              Bisphenol A-ethylene oxide adduct (1/6 molar ratio)                                                       146.6                                             Benzyldimethylamine         2.0                                               TEXANOL                     26.7                                              Lactic acid                 3.8                                               INDOPOL L-14                31.8                                              2-phenoxyethanol            166.5                                             Polyurethane crosslinker.sup.1                                                                            605.4                                             Dimethylethanolamine lactic acid salt as used                                                             52.1                                              in Example F                                                                  Dimethylcyclohexylamine lactic acid salt as used                                                          84.1                                              in Example F                                                                  GEIGY AMINE C               7.5                                               Deionized water             70.0                                              ______________________________________                                         .sup.1 Polyurethane crosslinker formed from halfcapping toluene               diisocyanate (80/20 2,4/2,6-isomer mixture) with 2ethoxyethanol and           reacting this product with trimethylolpropane in a 3:1 molar ratio. The       polyurethane crosslinker is present as a 70 percent solids solution in        2ethoxyethanol.                                                          

The procedure for preparing the cationic resinous composition was asgenerally described in Example F. The increase in epoxy equivalent wasfrom about 550 to 1220. The resinous mixture had a resin solids contentof 32 percent and contained 0.348 milliequivalents of quaternaryammonium base group per gram of resin solids.

Additive Example H

The following example shows the preparation of apolyepoxidepolyoxyalkylenediamine adduct. The adduct was made as anadditive for subsequent addition to a cationic electrodeposition bath toprovide better appearance in the cured coating.

In preparing the adduct, a polyepoxide intermediate was first preparedfrom condensing EPON 829 and bisphenol A as follows:

    ______________________________________                                        Ingredients    Parts by Weight                                                ______________________________________                                        EPON 829       136.1                                                          Bisphenol A    39.6                                                           2-butoxyethanol                                                                              52.3                                                           ______________________________________                                    

The EPON 829 and bisphenol A were charged to a reaction vessel under anitrogen blanket and heated to 70° C. to initiate an exotherm. Thereaction mixture was allowed to exotherm and held at 180° C. for 1/2hour. The reaction mixture was cooled to 160° C. and the 2-butoxyethanoladded to give a solids content of 75 percent and an epoxy equivalent of438 (based on solids).

A polyoxypropylenediamine having a molecular weight of 2000 andcommercially available from Jefferson Chemical Company as JEFFAMINED-2000 was reacted with the polyepoxide intermediate described above asfollows:

    ______________________________________                                        Ingredients        Parts by Weight                                            ______________________________________                                        JEFFAMINE D-2000   132.7                                                      Polyepoxide intermediate                                                                         67.4                                                       2-butoxyethanol    2.4                                                        Polyurethane crosslinker.sup.1                                                                   174.5                                                      Acetic acid        3.9                                                        Surfactant of Example B                                                                          7.4                                                        Deionized water    459.0                                                      ______________________________________                                         .sup.1 Polyurethane crosslinker formed from halfcapping toluene               diisocyanate (80/20 2,4/2,6-isomer mixture) with 2butoxyethanol and           reacting this product with trimethylolpropane in a 3:1 molar ratio. The       crosslinker is present as a 70 percent solids solution in methyl isobutyl     ketone and butanol (9:1 weight ratio).                                   

The JEFFAMINE D-2000 was charged to a reaction vessel under a nitrogenatmosphere and heated to 90° C. The polyepoxide intermediate was addedover the period of about 1/2 hour. At the completion of the addition,the reaction mixture was heated to 130° C., held for 3 hours, followedby the addition of the 2-butoxyethanol and polyurethane crosslinker. Thereaction mixture was then solubilized by blending with acetic acid, thesurfactant and deionized water. The adduct had a solids content of 35.5percent.

Example I

The adduct of Example H was combined with epsilon-caprolactam (forimproved rheology) as follows: T1 Ingredients? Parts by Weight? Adductof Example H 800.0 Epsilon-caprolactam 140.0 Deionized water 260.0

The caprolactam was heated to 80° C. to melt it and mixed with theadduct. The mixture was then thinned with deionized water.

Paints

The following Examples (1-6) show the preparation of paints from thecationic electrodepositable coating vehicles, pigment pastes andadditives described above. The paints were made by mixing theingredients together with low shear agitation. The paints wereelectrodeposited onto various steel substrates.

The wet films were cured at elevated temperatures, the thickness of thecoatings measured and the cured coatings evaluated for water and saltspray corrosion resistance. The results are shown in Table I appearingat the end of Example 6.

EXAMPLE 1

A cationic electrodepositable paint was prepared from the cationic resinof Example A. The resin was combined with a tin catalyst, pigmented withclay, basic lead silicate, carbon black, and strontium chromate, andthinned with deionized water.

The paint in the form of an electrodeposition bath had a solids contentof 20 percent, a pigment-to-vehicle ratio of 0.2/1.0, a pH of 6.6 and arupture voltage of 320 volts at ambient temperature.

Zinc phosphate pretreated and untreated steel panels were cathodicallyelectrodeposited in the bath at 78° F. (26° C.) for 2 minutes at 200volts.

EXAMPLE 2

A cationic electrodepositable paint was prepared by blending 1430 gramsof the cationic resin of Example A and 261 grams of the additive ofExample I. The blend was combined with a tin catalyst, pigmented withclay, titanium dioxide, basic lead silicate and carbon black, andthinned with deionized water.

The paint in the form of an electrodeposition bath had a solids contentof 20 percent, a pigment-to-binder ratio of 0.2/1.0 and a pH of 6.65.Zinc phosphate pretreated and untreated steel panels were cathodicallyelectrodeposited in the bath at 250 volts (zinc phosphate) and 275 volts(untreated steel) for 2 minutes at a bath temperature of 78° F. (26°C.).

EXAMPLE 3

A cationic electrodepositable paint was prepared by blending 1575 gramsof the cationic resin of Example B and 174 grams of the additive ofExample H. The blend was combined with a tin catalyst, pigmented withclay, titanium dioxide, basic lead silicate and carbon black, andthinned with deionized water.

The paint in the form of an electrodeposition bath had a resin solidscontent of 20 percent, a pigment-to-binder ratio of 0.2/1.0.

Zinc phosphate pretreated and untreated steel panels were cathodicallyelectrodeposited in the bath at 225 volts for the zinc phosphate and 175volts for the untreated steel for 2 minutes at a bath temperature of 78°F. (26° C.).

EXAMPLE 4

A cationic electrodepositable paint was prepared by blending 1437 gramsof the cationic resin of Example C and 174 grams of the additive ofExample H. The blend was combined with a tin catalyst, pigmented withclay, titanium dioxide, basic lead silicate and carbon black, andthinned with deionized water.

The paint in the form of a cationic electrodeposition bath had a resinsolids content of 20 percent, a pigment-to-binder ratio of 0.2/1.0, a pHof 6.5 and a rupture voltage of 355 volts at 26° C. The resin also had aGM throwpower of 111/4 inches measured at 300 volts at 26° C. Zincphosphate pretreated and untreated steel panels were cathodicallyelectrodeposited in the bath at 250 volts at 26° C. for 2 minutes.

EXAMPLE 5

A cationic electrodepositable paint was prepared by blending 1482 gramsof the cationic resin of Example D and 174 grams of the additive ofExample H. The blend was combined with a tin catalyst, pigmented withclay, titanium dioxide, basic lead silicate and carbon black, andthinned with deionized water.

The paint in the form of a cationic electrodeposition bath had a solidscontent of 20 percent, a pigment-to-binder ratio of 0.2/1.0, a pH of 6.5and a rupture voltage of 350 volts at 26° C. Zinc phosphate pretreatedand untreated steel panels were cathodically electrodeposited in thebath at 275 volts for 2 minutes at a bath temperature of 26° C.

EXAMPLE 6

A cationic electrodepositable paint was prepared by blending 1482 gramsof the cationic resin of Example E and 174 grams of the additive ofExample H. The blend was combined with a tin catalyst, pigmented withclay, titanium dioxide, basic lead silicate and carbon black, andthinned with deionized water.

The paint in the form of a cationic electrodeposition bath had a solidscontent of 20 percent, a pigment-to-binder ratio of 0.2/1.0. Zincphosphate pretreated and untreated steel panels were cathodicallyelectrodeposited in the bath at 300 volts for 2 minutes at a bathtemperature of 26° C.

                                      TABLE I                                     __________________________________________________________________________    Curing Schedules and Evaluation of Cured Coatings of Examples 1-6             for Salt Spray Corrosion Resistance.sup.1 and Water Resistance.sup.2          Cure                         Scribe                                           Temperature Time             Creepage.sup.1                                                                      Water Soak.sup.2                           Example                                                                            °F. (°C.)                                                              (min.)                                                                            Substrate    (inches)                                                                            Top Coat.sup.3                                                                      Primer                               __________________________________________________________________________    1    325 (163)                                                                            20  zinc phosphate pretreated                                                                   1/32 --    --                                        "      "   untreated steel                                                                             1/32 --    --                                   2    325 (163)                                                                            20  zinc phosphate pretreated                                                                  <1/32 9     10                                        "      "   untreated steel                                                                            <1/32 --    --                                   3    300 (149)                                                                            20  zinc phosphate pretreated                                                                  <1/32 6     10                                        "      "   untreated steel                                                                             3/64 4      8                                   3    325 (163)                                                                            20  zinc phosphate preheated                                                                   < 1/32                                                                              8     10                                        "      "   untreated steel                                                                             1/32 8      9                                   3    350 (177)                                                                            20  zinc phosphate pretreated                                                                  <1/32 .sup. 4.sup.a                                                                       10                                        "      "   untreated steel                                                                             11/16                                                                              7       9                                  4    325 (163)                                                                            20  zinc phosphate pretreated                                                                  <1/32 8     10                                        "      "   untreated steel                                                                            <1/32 --    --                                   5    325 (163)                                                                            20  zinc phosphate pretreated                                                                  <1/32 5     10                                        "      "   untreated steel                                                                            <1/32 --    --                                   6    325 (163)                                                                            20  zinc phosphate pretreated                                                                  <1/32 5     10                                        "      "   untreated steel                                                                             3/32 --    --                                   __________________________________________________________________________     .sup.1 Coated panels scribed with an "X" and exposed to a salt spray fog      as described in ASTM D117. After 14 days, the panels were removed from th     testing and the scribe mark taped with masking tape, the tape pulled off      at a 45° angle and the creepage from the scribe line measured.         Creepage is the area where the coating has lifted from the panel surface.     .sup.2 Coated panels soaked in water at 120°  F. (49° C.)       for 24 hours, removing the panel from the water, permitting it to stand a     room temperature for 1 hour, followed by crosshatching the coated surface     taping the crosshatch area with masking tape and pulling the masking tape     off at a 45° angle. Ratings were assigned a value of 1 to 10           depending on how much coating was removed with the masking tape, with 1       being the worst and 10 the best.                                              .sup.3 The top coat was deposited from a nonaqueous dispersion acrylic        polymer white coating composition available from Cook Paint and Varnish       Company as WEA 5111. The coating composition as obtained was reduced with     a 50/50 mixture of xylene and an aromatic blend of solvents having a          boiling point of 155 to 184 so as to obtain a 17second viscosity measured     with a No. 4 Ford cup.                                                   

EXAMPLE 7

A cationic electrodepositable paint was prepared by blending 1061.8grams of the cationic resin of Example F with 386 grams of CYMEL 1156which is an etherified melamine-formaldehyde commercially available fromAmerican Cyanamid Company. The blend was pigmented with carbon black,aluminum silicate and titanium dioxide, and thinned with deionizedwater.

The paint in the form of an electrodeposition bath had apigment-to-binder ratio of 0.4/1.0, and contained 15 percent by weightsolids. Zinc phosphate pretreated and untreated steel panels werecathodically electrodeposited in the bath at 250 volts at a bathtemperature of 65° F. (18° C.). The wet films were baked at 400° F.(204° C.) for 20 minutes. The coated panels were subjected to testingfor detergent resistance as provided by ASTM D-2248 and after 1150hours, the coatings retained good appearance.

EXAMPLE 8

A cationic electrodepositable paint was prepared from the cationic resinof Example G. The resin was pigmented with carbon black, aluminumsilicate and titanium dioxide, and thinned with deionized water.

The paint in the form of an electrodeposition bath had apigment-to-binder ratio of 0.4/1.0 and contained 15 percent by weightsolids.

Zinc phosphate pretreated steel panels were cathodicallyelectrodeposited in the bath at 250 volts for 11/2 minutes at a bathtemperature of 80° F. (27° C.). The wet films were cured at 400° F.(204° C.) and subjected to detergent resistance testing as describedabove. After 528 hours, the coatings retained good appearance.

We claim:
 1. In a method of coating a conductive substrate serving as acathode in an electrical circuit comprising said cathode and an anodeimmersed in an aqueous electrodepositable coating composition, saidmethod comprising passing electric current between said cathode and saidanode to cause a coating to deposit on said cathode, said coatingcomposition comprising a resin which contains cationic base groups andwhich is formed from reacting a polyepoxide resin with a cationic basegroup former, the improvement comprising a polyepoxide resin which isformed from reacting a polyepoxide with a polyether polyol; saidpolyether polyol formed from reacting:(A) a cyclic polyol with (B)ethylene oxide or a mixture of ethylene oxide and an alkylene oxidehaving 3 to 8 carbon atoms in the alkylene chain; the equivalent ratioof (B) to (A) being within the range of 3 to 20:1.
 2. The method ofclaim 1 in which the cationic resin contains active hydrogens and ispresent with a curing agent which is stable in the presence of activehydrogens but which is reactive with the active hydrogens at elevatedtemperatures to form a cured product.
 3. The method of claim 2 in whichthe curing agent is a capped organic polyisocyanate.
 4. The method ofclaim 3 in which the organic polyisocyanate is fully capped.
 5. Themethod of claim 2 in which the curing agent is an aminoplast.
 6. Themethod of claim 1 in which the aqueous dispersion contains 1 to 50percent by weight of cationic resin.
 7. An article coated by the methodof claim 1.